1. Field of the Invention
The present invention relates to a message relaying scheme that is suitable for constructing a ultra-high-speed message relaying system.
2. Description of the Background Art
In recent years, in conjunction with the explosive spread of the so called Internet, the throughput improvement in a connection-less network for leading the so called IP message to a desired terminal has become a major technical problem.
In the case of connection-less network, the end-to-end communications are provided as each routing processing device refers to a destination address assigned to each individual message and transfers the individual message independently to a desired output path. For this reason, it is possible to utilize the bandwidth of each physical link more flexibly compared with the connection-oriented network, and there is an advantage in that the bandwidth of the physical link can be utilized efficiently in a situation where traffics transmitted by terminals are highly bursty, which is characteristic of applications such as WWW for which the spontaneity in the continuous information communications has low importance.
On the other hand, there is a problem in that the amount of calculations required to the routing processing device at a time of routing individual message is overwhelmingly large compared with the connection-oriented network so that it is difficult to realize a high throughput routing processing device.
This problem stems both from the large amount of calculations that is inherently associated with the connection-less communications due to the fact that a physical link to which each message should be outputted must be determined whenever a message arrives, and from the physical constraint associated with electric circuits that it is very difficult to construct ultra-high-speed signal transmission paths using electric signals. This problem becomes particularly noticeable in the case where the physical link accommodated by the routing processing device uses various protocols such as Ethernet, PPP, ATM and SDH, or in the case of providing the so called multicast connection in which a single message is to be copied and lead to plural output paths.
A conventionally adopted method for resolving this problem is one in which a plurality of routing processing devices are directly connected by a physical link group and operated such that they can be regarded as a single routing processing device as a whole, as shown in FIG. 57.
In outline, the ultra-high-speed message relaying system shown in FIG. 57 operates as follows. When a message is entered from a connection-less network 103-i to a routing processing device 102-i, the routing processing device 102-i extracts a destination address of the entered message, obtains a next hop address of that message by referring to a routing table which has the extracted destination address as a key, selects a physical link corresponding to that next hop address from physical links connected to the own device, and transmits the message toward that physical link. When this operation is carried out by every routing processing device 102-i, the message transfer between connection-less networks 103-i via a plurality of routing processing devices 102-i can be realized. At this point, the routing processing at each routing processing device 102-i is carried out independently from any other routing processing device 102-j so that the throughput of the routing processing for the system as a whole can be improved.
However, this scheme directly arranges the physical links among the routing processing devices 102-i so that the bandwidth of the communication path between each connected routing processing devices 102-i becomes fixed and the transmission bandwidth allocation between the routing processing devices cannot follow the dynamic change of traffics among the connection-less networks. For this reason, this scheme has a problem that it is impossible to utilize the bandwidth of the physical link efficiently.
In particular, in the case of applications such as WWW in which the user's access target changes frequently, messages transmitted from one routing processing device 102-i are not uniformly distributed over other connection-less networks so that the bandwidth required between the routing processing devices 102-i and 102-j changes largely in time, but this scheme cannot provide the required bandwidth between the routing processing devices 102-i and 102-j in such a situation. Consequently, this scheme has a problem that the comfortable communications cannot be provided to users because a length of a queue for holding messages to be transmitted to a physical link with insufficient bandwidth that is connected to a connection-less network 103-i becomes long so that the message delay time becomes extremely long.
As described, the conventional routing processing device has been associated with a problem that it is difficult to realize a high throughput routing processing device because of the large amount of calculations that is inherently associated with the connection-less communications and the physical constraint associated with electric circuits. This problem becomes particularly noticeable in the case where the routing processing device accommodates various protocols or in the case of providing the multicast connection.
In addition, the conventional ultra-high-speed message relaying system formed by combining the routing processing devices, the transmission bandwidth allocation between the routing processing devices is fixed so that the bandwidth cannot be allocated by following the traffic pattern that continually changes in time, and therefore there has been a problem that the comfortable communications cannot be provided to users.